It turns out there's nothing cool about the dark side of the Force. In fact, it's blazing hot.

But is it hot enough to get into Guinness?

Longmont resident Jonathan Rice hopes so. And he backed up that hope Sunday with a run through a 129-degree Death Valley in a Darth Vader suit. Complete with mask and cape.

"It's completely crazy, but it's really fun," said Laura Greenfield, a friend who's gone with him in previous years as a Princess Leia-dressed support crew.

It started in 1996, when Rice visited Death Valley, Calif., with a friend and was won over by the beauty and the challenge of heat running. He had the friend drive ahead half a mile or even a mile so he could run to catch up.

It almost proved too challenging. Another car turned up on the narrow road; Rice's friend had to drive three miles before he could pull over.

"There I was with no water, completely ill-prepared," Rice said. "You can do a solo run if you stay within a couple miles of your crew, but even a four-mile run can be too hot. If you're not experienced, it will kill you."

Rice's reaction was "When can we do this again?"

Heat running became a regular hobby. But after a while, he said, even Death Valley became too easy. He needed to raise the bar.

A black heat-attracting costume would do it, he decided. Especially one with a face mask to prevent the limited cooling that comes from a runner's own breath.

"So," Rice said, "Darth Vader it was."

That was about three years ago. Now, it's starting to draw a crowd. In addition to Greenfield's Leia, a handful of other runners and fans show up as R2-D2, Yoda or some other denizen of a galaxy far, far away. This year's support driver even dressed as the hairy Chewbacca -- a costume that works only when you're sitting in the air-conditioned car.

If it sounds crazy, Rice would agree. His own website (darthvalley.com) warns imitators that they do so at their own risk, and those risks include dehydration, heatstroke, heart attack, "death, death, more death and getting a purple face."

"This is a ludicrously dangerous endeavor," he warns on the website. "I don't support you doing it. I don't even really support me doing it."

While Rice does longer bouts of heat running, the "Darth Valley Challenge" is always a one-mile sprint, done as rapidly as possible. Sunday, he ran it in about 6:36; his personal best is 6:13.

But speed was a secondary goal this year. Rice's hope is to make the Guinness Book of World Records for the hottest verified run. For precision, he started at 4 p.m., the moment Death Valley's temperature is recorded by the National Weather Service.

It'll be a while before he finds out if the record is his. But even without it, Rice has gained a fair amount of renown.

"I have had people call up and say 'Dude, is that you on Instagram?" he laughed.

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